Pulse width modulation (PWM) systems are used to generate analog signals from digital data. PWM signals can be used to drive an H-bridge or similar device (such as an amplifier or other buffer circuit) to achieve high power and high efficiency amplification. An ideal H-bridge is simply a buffer that reproduces the digital waveforms with higher output amplitude. Preferably, the buffer has a fixed delay, providing edge transitions (rising or falling) at its output at a fixed time offset from the input.
Unfortunately, the propagation delay of a practical H-bridge implementation may be variable and/or signal dependent. In Class D amplifiers, such as those used in audio applications, propagation delay variations through an H-bridge or buffer circuit represents a non-linearity. Such a non-linearity can result in degraded Total Harmonic Distortion of the audio signal. Additionally, even if circuitry is introduced to reduce or eliminate such propagation delay variations, component mismatches within such circuitry can also introduce a non-linearity. If spectral energy spreading techniques have been applied to the PWM signal, such non-linearities due to propagation delay variation and/or component mismatches can cause high frequency noise to fold into the lower frequencies of the audio band or into the frequency band of interest, resulting in harmonic distortion or degraded signal-to-noise ratio (SNR).